1. Field of the Invention
The present invention relates to apparatus for circulating document sheets to an exposure station, for example the exposure station of a copier/duplicator or the like. More specifically, the invention relates to a recirculating document feeder adapted to operate in several different modes depending upon the number of sheets in the document to be copied.
2. Description of the Prior Art
Recirculating document feeders are well known in the prior art. Commonly assigned Reissue Patent No. RE 27,976 entitled DOCUMENT FEEDER which issued on Apr. 23, 1974, discloses such a feeder in which document sheets are fed from a supply to an exposure station and back to the supply. Commonly assigned British Pat. No. 1,492,466 entitled RECIRCULATING SHEET FEEDER FOR DOCUMENT COPYING, which issued on Mar. 22, 1978, discloses a recirculating document feeder wherein document sheets are placed in a tray with the document sheets in the normal page sequence order and with first sheet of the document facing upwardly. The sheets are then removed from the tray, bottom sheet first, and fed to a platen where the sheet is exposed for copying by an associated copier. The document sheet is then fed back to the tray and on top of other document sheets in the tray. This cycle is repeated until all of the document sheets are exposed one or more times, and collated sets of copies are produced in the copier. The associated copier/duplicator is preferably controlled by a microprocessor as disclosed, for example in commonly assigned U.S. Pat. No. 3,914,047 which issued on Oct. 21, 1975 in the name of W. E. Hunt, Jr., et al and is entitled SYNCHRONIZING CONTROL APPARATUS FOR ELECTROPHOTOGRAPHIC APPARATUS UTILIZING DIGITAL COMPUTER. Preferably the computer control apparatus for the copier is also coupled to the recirculating feeder to obtain coordinated operation. Two patents disclosing this relationship are commonly assigned U.S. Pat. No. 4,076,408, which issued Feb. 28, 1978 in the names of M. G. Reid, et al, entitled COLLATING DOCUMENT FEEDER WITH MULTIPLE FEED DETECTOR, and U.S. Pat. No. 4,078,787, which issued on Mar. 14, 1978 in the names of L. E. Burlew, et al, entitled AUTOMATIC FEEDER AND COPIER OPERATIONS. Various modes of operation are disclosed in the before mentioned patents. In one mode of operation (the so-called collate mode of operation) a plurality of document sheets placed in a supporting tray are fed seriatim from the tray to an exposure position at the copier platen and copied once before being returned onto the top of the stack in the tray. This mode of operation produces one or multiple sets of collated copies in the copier. In the second mode of operation (the so-called non-collate mode of operation) a document sheet is fed to the exposure station at the platen and held in place while multiple copies of that single document sheet are copied. The document sheet is then returned to the supporting tray.
Other types of recirculating document feeders are known, including those feeders which utilize vacuum sheet transport means for all or a portion of the movement of the document sheets. In this regard, reference is made to U.S. Pat. No. RE 29,178 and to U.S. Pat. No. 3,562,532. The latter patent relates to a variable speed drive transmission associated with a vacuum feed mechanism which operates to vary the spacing of sheets drawn onto the vacuum belt. Another automatic feeding device utilizing a vacuum sheet transport is shown and described in Disclosure No. 15,056 which appears at pages 47 and 48 of the October, 1976 edition of Research Disclosure, a publication by Industrial Opportunities, Ltd., Homewell, Havant, Hampshire, PO91EF, United Kingdom. The feeder device disclosed in the latter publication comprises a vacuum feeder which separates the bottom most sheet from the stack and furnishes it to a plurality of vacuum belts. The belts deliver the sheets seriatim to a platen for exposure and then return the sheet to the top of the stack in the tray.